The invention relates to a semiconductor component and a method for producing the same.
Semiconductor components including Schottky metal contacts are known from the document DE 103 26 739 B3. In the case of the known component, charge compensation zones are likewise provided in the drift path. In the case of the known semiconductor component, the charge compensation zones are configured in such a way that premature commencement of bipolar injection is suppressed. In order to set the commencement of the charge carrier flooding in forward operation and thus the overcurrent strength, a Zener diode is additionally also provided in the case of the known semiconductor component including Schottky metal contacts.
Schottky diode contact junctions, on the one hand, and pn and also pin diode junctions, on the other hand, fundamentally differ from one another with regard to their on-state behavior and their switching behavior. Schottky diode junctions are distinguished by a unipolar current transport at a low threshold voltage of the order of magnitude of approximately 0.2 to 0.4 volt and enable very fast switching. At high current densities, however, the forward voltage of Schottky diodes increases greatly. By contrast, pin diodes, owing to their bipolarity, utilize the injection of minority charge carriers and also of majority charge carriers in their base zone when a specific threshold voltage of approximately 0.7 V is reached in order to reduce the base resistance in forward operation. A type of plasma flooding occurs here in the on-state case of the pin diode as a result of the injection of the minority charge carriers and the majority charge carriers. This plasma flooding that lowers the base resistance adversely affects the switching losses that arise, however, when the pin diode is switched off, since the introduced charge carriers have to be fully depleted and this depletion has to take place at a negative voltage already present.
Consequently, Schottky diode junctions are advantageous with regard to their switching behavior, but have disadvantages at high current densities. Furthermore, the use of Schottky diode junctions in the range of higher reverse voltages is limited by the large proportion of the reverse current in the total losses. This is because in the case of Schottky diodes the reverse current is fundamentally determined by the magnitude of the electric field present at the metal-semiconductor junction. Moreover, for unipolar components that operate with Schottky contacts, a more than quadratic relationship holds true between their forward resistance and their blocking capability. This relationship also imposes relatively narrow limits on the design of semiconductor components including Schottky contacts.
The document mentioned above proposes a plurality of solutions for overcoming disadvantages for semiconductor components including Schottky metal contacts. Firstly, it is proposed to use superjunction structures, about which it is known that low on resistances can be combined with a high breakdown voltage on account of the arrangement of drift zones of a first conduction type and adjacent charge compensation zones of a complementary conduction type with respect to the first conduction type. As mentioned above, Schottky diode junctions exhibit a significantly lower threshold voltage than pn or pin diodes of the same semiconductor material. Furthermore, the Schottky diode junctions have the advantage of a vanishingly small reverse recovery charge.
However, on account of the low doping of the drift zones and the corresponding length necessary for achieving the high reverse voltage, diodes of this type have a high forward resistance. A combination, however, such as is already known from the document mentioned above, of Schottky diodes with superjunction drift path structures yields, in principle, semiconductor components having comparatively low resistance in conjunction with a constantly high reverse voltage.
In the case of these structures, the problem nevertheless remains that minority charge carrier injection already commences at a low forward voltage of the order of magnitude of the threshold voltage of a bipolar diode, such that a semiconductor component of this type reacts more or less like a bipolar diode. Thus, even with the combination of a superjunction semiconductor component and a Schottky metal contact as first metallization structure, the advantage of the vanishing reverse recovery charge is nullified.
One of the solutions disclosed by the document mentioned above provides for the first metallization structure to have Schottky metal contacts including different materials for the charge compensation zones and for the drift zones of a superjunction semiconductor component. However, this measure functions only in a very limit forward voltage range. A second known solution consists, then, in providing an additional pn junction between an anode contact of a diode and the charge compensation zones, which prevents charges from passing into the charge compensation zones during the on-state phase.
However, parasitic npn transistors with an open base arise in the case of this solution, which significantly reduces the breakdown voltage of such semiconductor components. A third known solution provides for providing an additional “threshold component” between the charge compensation zones and the anode contact, which makes it possible for a current flow to take place through the charge compensation zones only at a specific threshold voltage. Zener diode structures or MOSFET structures with short-circuited gate-drain terminals can be used for this purpose.
The document DE 103 37 457 B3 furthermore discloses transistor components having an improved reverse current behavior in which the abovementioned structures with Schottky metal contacts are used.
For these and other reasons, there is a need for the present invention.